There is an edge case interaction between Comcast IPv4 [https://en.wikipedia.org/wiki/Differentiated_services DSCP] and improper condition handling in the [https://en.wikipedia.org/wiki/Wireless_Multimedia_Extensions WMM] driver in certain '''Linksys/Cisco eSeries''' routers (and possibly others as well) which results in very low download speeds. This issue can appear in both stock and third-party (DD-WRT) firmware, although Cisco appears to have at some point released new WMM drivers that largely resolve the issue in current stock firmware.

There is an edge case interaction between Comcast IPv4 [https://en.wikipedia.org/wiki/Differentiated_services DSCP] and improper condition handling in the [https://en.wikipedia.org/wiki/Wireless_Multimedia_Extensions WMM] driver in certain '''Linksys/Cisco eSeries''' routers (and possibly others as well) which results in very low download speeds. This issue can appear in both stock and third-party (DD-WRT) firmware, although Cisco appears to have at some point released new WMM drivers that largely resolve the issue in current stock firmware.

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Unlike other service providers, IPv4 packets from the Comcast network are configured with DSCP 8, Priority higher than Default/Routine (0).

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The cause is that IPv4 packets from the Comcast network are configured with DSCP 8, which the driver handles improperly, whereas other providers typically use DSCP 0, which the driver handles properly. (Both are valid values.)

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== Symptoms ==

== Symptoms ==

Download speeds are normal with ''current'' stock firmware, and on ''wired'' connections with DD-WRT firmware, but are much lower (possibly even less than 1 Mbps) on ''wireless'' connections with DD-WRT firmware even with strong signal.

Download speeds are normal with ''current'' stock firmware, and on ''wired'' connections with DD-WRT firmware, but are much lower (possibly even less than 1 Mbps) on ''wireless'' connections with DD-WRT firmware even with strong signal.

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Because DSCP pertains to QoS, it's possible this problem might only exist ''when QoS is enabled'' (and go away when QoS is disabled), but this has not been confirmed.

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To see if you are getting the problematic DSCP, you can look at your downloaded IPv4 packets with [http://www.wireshark.org/ Wireshark], preferably directly connected to WAN, but you should see them even on Wi-Fi. (See [http://netspoon.wordpress.com/2012/09/08/add-dscp-column-in-wireshark/ Add DSCP Column in Wireshark])

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To see if you are getting the problematic DSCP, look at your downloaded IPv4 packets with [http://www.wireshark.org/ Wireshark], preferably directly connected to WAN, but you should see them even on Wi-Fi. (See [http://netspoon.wordpress.com/2012/09/08/add-dscp-column-in-wireshark/ Add DSCP Column in Wireshark])

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== Testing ==

== Testing ==

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To test this fix, open a Telnet or SSH connection to DD-WRT, and run the following commands (copy and pasting to avoid typos):

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To test this fix, open a Telnet or SSH connection to DD-WRT, and run the following commands (copy and paste to avoid typos):

insmod xt_DSCP.ko

insmod xt_DSCP.ko

Line 25:

Line 23:

Assuming there are no errors, check download speed on wireless.

Assuming there are no errors, check download speed on wireless.

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You may need to change ''vlan2'' depending on your particular setup.

== Configuration ==

== Configuration ==

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To save the fix so it survives reboots, first navigate to ''Administration'' > ''Commands''

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To save the fix so it survives reboots, navigate to ''Administration'' > ''Commands''

Current revision

Contents

There is an edge case interaction between Comcast IPv4 DSCP and improper condition handling in the WMM driver in certain Linksys/Cisco eSeries routers (and possibly others as well) which results in very low download speeds. This issue can appear in both stock and third-party (DD-WRT) firmware, although Cisco appears to have at some point released new WMM drivers that largely resolve the issue in current stock firmware.

The cause is that IPv4 packets from the Comcast network are configured with DSCP 8, which the driver handles improperly, whereas other providers typically use DSCP 0, which the driver handles properly. (Both are valid values.)

Download speeds are normal with current stock firmware, and on wired connections with DD-WRT firmware, but are much lower (possibly even less than 1 Mbps) on wireless connections with DD-WRT firmware even with strong signal.

To see if you are getting the problematic DSCP, you can look at your downloaded IPv4 packets with Wireshark, preferably directly connected to WAN, but you should see them even on Wi-Fi. (See Add DSCP Column in Wireshark)